The present invention relates to an image recording apparatus for recording an image information on a photosensitive recording medium.
Image information may be recorded on a photo-sensitive pressure-sensitive recording sheet in different ways. For example, image information may be scanned and exposed directly to a photosensitive pressure-sensitive recording sheet by using switchable light such as a laser beam. Alternatively, light information may be written on a photosensitive pressure-sensitive recording sheet with a microshutter such for example as a liquid crystal light shutter being disposed between the sheet and a continuously energized lamp. These methods however have the following problems:
With respect to the former method, photosensitive pressure-sensitive recording sheets that are presently manufactured have spectral sensitivities below a wavelength .lambda.=475 nm. Therefore, the laser beam source for scanning and exposing the sheets should be an argon laser beam source (wavelength .lambda.=351 nm), a krypton laser beam source (wavelength .lambda.=351 nm), a helium-cadmium laser beam source (wavelength .lambda.=325 nm), or an ultraviolet gas laser. These laser devices are however large in size and expensive.
As regards the latter method, where a liquid crystal light shutter is employed as the microshutter, the liquid crystral itself is deteriorated by ultraviolet radiation.
A picture image recording apparatus designed to eliminate the aforesaid difficulties is disclosed in Japanese Patent Application Kokai No. 62-231965 (corresponding to U.S. Pat. Application No. 32,865, U.S. Pat. No. 4,772,922).
In the disclosed picture image recording apparatus, a latent image corresponding to a picture image on an original is formed on a transparent photosensitive body as a latent image carrier, and a light-shielding material is coated on the latent image. A photosensitive pressure-sensitive sheet and an exposure device are disposed one on each side of the transparent photosensitive body, and the sheet is exposed to light from the exposure device through the light-shielding material and the transparent photosensitive body.
The sheet carries a multiplicity of microcapsules on its surface. The microcapsules can be solidified by exposure to light, but remains soft unless exposed to light. The microcapsules as hardened by exposure to light are not ruptured when pressure is applied to the sheet. Those microcapsules are soft because light is prevented from being applied thereto by the light-shielding material are however ruptured by such pressure. The recording sheet therefore develops color by a coloring agent contained in the microcapsules. Therefore, a picture image corresponding to the latent image on the transparent photosensitive body is formed on the sheet. The developed picture image is identical to the picture image on the original. Thus, the picture image on the original is now duplicated.
The picture image recording apparatus described above is free from the problems of the conventional apparatus using a photosensitive pressure-sensitive sheet, i.e., large size of the exposure scanning means and deterioration of the microshutter. However, in the recording apparatus, more improved final output image has been demanded.
Another type of image recording apparatus has been developed in the art. One such image recording apparatus is disclosed in commonly assigned U.S. Pat. Application No. 50,313 filed on May 14, 1987, U.S. Pat. No. 4,810,614, this copending application corresponds to Japanese patent application Kokai No. 62-269961 published on Nov. 24, 1987.)
According to the disclosed apparatus, a first exposure unit is provided on a photosensitive drum so as to provide a latent image on the drum in accordance with an image information. Further, a first developing unit is provided to form light shieldable visible image corresponding to the latent image with using toners. The toner image is then transferred to a light transmission member formed of an endless transparent insulation film by means of a transfer unit. The transmission member carrying thereon the light shieldable visible toner image is delivered onto a photosensitive recording medium. When the toner image is comming to a given position, a second exposure unit irradiates diffusion light, so that a latent image is formed on the photosensitive recording medium through the visible image on the transmission member. Thus formed latent image on the photosensitive recording medium then becomes a visible or output image when the photosensitive recording medium passes through a second developing unit consisting of pressure developing rollers.
According to the image recording apparatus disclosed in the copending application Ser. No. 50,313, the photosensitive drum forms the light shieldable toner image whose dimension is equal to that of an original image information. The visible toner image is then transferred onto the transmission member, and the latter is in close contact with the photosensitive medium for the light-exposure so as to form the latent image thereon. The latter latent image on the photosensitive sheet also has the size equal to the light shieldable toner image on the transmission member. However, demand has been made for providing highly sophisticated final output image on the photosensitive recording medium, and another demand resides in the provision of a compact apparatus yet providing desirable output image.
Still another image recording apparatus is disclosed in commonly assigned U.S. Pat. Application Ser. No. 157,740 filed Feb. 18, 1988, U.S. Pat. No. 4,785,346.
In the disclosed image recording apparatus, image information to be recorded is reduced in size by a control unit, and then an electrostatic latent latent image is formed on a photosensitive drum based on the image information by a first exposure unit. The latent image on the photosensitive drum is developed with toner by a first image developing unit, and the developed light shieldable toner visible image is transferred onto a transmissive member comprising a transparent insulative film by an image transfer unit. The transferred image is delivered into a position above a photosensitive recording sheet upon movement of the transmissive member. Diffusive light is applied to the transmissive member which bears the light-shielding developed image by a second exposure device. The light which has passed through the developed image is enlarged by an enlarging means such as a lens and applied to the photosensitive recording sheet to form a latent image thereon. The latent image is then developed into a visible image by a second image developing unit comprising pressure developing rollers.
According to the above process, therefore, the light-shielding image which is smaller in size then the original image information is first formed on the transparent film, and thereafter the image on the transparent film is enlarged in size and formed on the photosensitive recording sheet thereby to produce a full-size image thereon which is equal in size to the original image information.
In the image recording apparatus disclosed in the copending U.S. Pat. Application Ser. No. 157,740, the image is first reduced at the first image developing device, so that the photosensitive drum as well as the transparent insulative film can have reduced size. And then the reduced image is enlarged to the original image size. Accordingly, the image recording apparatus disclosed in USSN 157,740 has advantage over the USSN 50,131 in that the latter should provide first light exposure and image developing units having dimensions sufficient to transfer the image having size always equal to that of the original image. In the USSN 157,740, because of the minimization of the first light exposure and image developing units, electrical charge to the photosensitive drum can be uniformly performed, and toner can be uniformly distributed over the peripheral surface of the drum because of its small peripheral area. Further, sufficient light exposure by means of a laser beam can be attained because of the small scanning length. Furthermore, the transparent sheet can also be minimized, so that it becomes much easier to control travelling condition thereof.
Even though the image recording apparatus according to USSN 157,740 can provide the above-described advantages, primary attention must still be drawn to the quality of the final output image formed on the photosensitive recording sheet. In this connection, in the apparatus disclosed in USSN 157,740, the resolution of the image (output image) on the photosensitive recording sheet is 1/(magnification) of the resolution of the image on the transparent film, since the smaller size is first formed on the transparent film and then enlarged by the enlarging means and formed on the photosensitive recording sheet. Therefore, even if the image formed by the first exposure and image developing units is of high resolution, the resolution of the final image is lower than the resolution of the image formed by the first exposure and image developing units since the image produced by the light applied from the second exposure unit is enlarged in size.
At present, various sheet sizes such as A4, B4, A3 sizes are available in large quantities in the market, and the image recording apparatus are no longer limited to use of any particular sheet size. In addition, finally produced images are required to be of high resolution which is by far important in nowadays trend, and hence the quality of final images governs the commercial success of image recording apparatus. Consequently, image recording apparatus, no matter whether they may be expensive or inexpensive, they should produce images of high resolution with good reproducibility for their success in the market.
Other copending U.S. Patent Applications commonly assigned have been filed bearing Ser. Nos. 184,576 filed Apr. 21, 1988, 156,744 filed Feb. 18, 1988 and 173,610 filed Mar. 25, 1988.